Comparison of laboratory and in situ reflectance spectra of Chang'e-5 lunar soil

Context. Reflectance spectra provide essential information on the mineralogical composition of a planetary surface. However, the spectral characteristics of lunar soil are significantly influenced by its photometric properties, coupled with space weathering and particle size.Aims. China's Chang'e-5 (CE5) mission returned lunar soil samples and obtained in situ spectra of the sampling site, enabling us to compare the laboratory and in situ analyses of the same sample.Methods. In this study, we measured the reflectance spectra of the bulk CE5 soil and two size fractions (<45 and 45-355 mu m) at various phase angles (41.3 degrees to 101.3 degrees).Results. The photometric properties of the CE5 samples exhibit back scattering, whereas an in situ measurement appears as forward scattering, indicating that in situ photometric experiments are always necessary for spectral exploration on the Moon. In addition, the scattering properties of the <45-mu m fraction are closer to the in situ spectral data, suggesting that the finer fraction could be more representative of pristine lunar soil. The maturity of CE5 soil is estimated to be submature to mature based on the spectral ratio between 750 nm and 950 nm.